Ruthenium catalyst supported on high-surface-area basic ZrO2 for ammonia synthesis

• The Ru/ZrO2-KOH with high activity for NH3 synthesis was prepared for the first time.
• The interaction of K and ZrO2 is different from those of K and Al2O3 or MgO.
• The abundant of basic sites can hence the dissociation of N over this catalyst.
• The activity of Ru/ZrO2-KOH increased first and then decreased with the reaction pressure.

The superbasic ZrO2 (ZrO2-KOH) with high surface area was prepared by reflux-digestion of ZrO(OH)2 gel in mother liquor and examined as a support promoting ammonia synthesis by particulate Ru. The TEM image of Ru/ZrO2-KOH catalyst indicates that the size of Ru particles is in the range of 1.5–3.2 nm, which is the optimum size of Ru particles for the maximum number of B5-type sites. Additionally, the characterizations including CO2-TPD, XPS and N2-TPD demonstrate that the Ru particles supported on ZrO2-KOH exhibit higher electron density compared to that of Ru/ZrO2 catalyst. As a result, the dissociative adsorption of N2 over Ru/ZrO2-KOH is more facile than that over Ru/ZrO2 catalyst. Thus, the Ru/ZrO2-KOH catalyst shows an excellent activity for ammonia synthesis especially under the conditions of low temperature and pressure. The highest reaction rate of Ru/ZrO2-KOH is 16.91 mmol/(g h) at 698 K and 3.0 MPa, which is much higher than that of various Ru catalysts supported on other supports.

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